This invention relates to cathode ray tube electron gun structures and more particularly to a discretely formed metallic member for supporting a cathode eyelet assembly in a single gun structure.
Single gun cathode ray tubes (CRTs) are manufactured for a variety of utilizations, as for example, monitor and computer graphic display terminals, monochrome television applications, and individual color projection tubes. Electron guns conventionally utilized therein are usually comprised of a plurality of sequentially cooperating electrode components held in spaced axial alignment by several longitudinal insulative rods or multiforms. Such integrated structures include an electron-emitting cathode structure positioned adjacent the first or control electrode or grid (Gl). In such single gun tubes, the control electrode is often in the form of a cup-shaped component having an aperture in the closed end thereof. The cathode is located inside the cup with the terminal emissive surface of the cathode oriented adjacent the aperture of the control electrode. A common arrangement for effecting positioning of the cathode relative to the Gl aperture has been by crimping or otherwise forming annular protrusions in the cathode eyelet adjacent upper and lower surfaces of an apertured supporting ceramic disc. This assembly is then seated against a precisely-positioned spacing member placed on the inner wall of the control electrode, whereupon a metallic retaining member is abutted against the ceramic and suitably affixed to the inner wall of the electrode to hold the assembly in place. This procedure is expensive in that it involves a multiplicity of parts and the accurate assembly thereof. Additionally, the spacers must be matched with the cathode-ceramic assemblies to achieve the proper spacing between the cathode emissive surface and the aperture of the control electrode. Furthermore, it has been found that, upon successive operational heatings, the cathode eyelet tends to loosen in the ceramic. This often generates a microphonic condition and promotes an increase of cathode temperature, which may be in the order of 50.degree. C. Both of these conditions are deleterious to tube operation and life.
In older multi-gun color CRT electron gun structures, each cathode assembly has been individually mounted using various support arrangements, such as that taught by Alan T. Kuryla in U.S. Pat. No. 3,351,792. However, in the present state of the art for single gun tube design, there is need for cathode support means which are suitable for single gun CRT constructions requiring strength, rigidity and durability, all in a miniaturized design.